1. Field of the Invention
The present invention relates to an inkjet recording method and an inkjet recording apparatus, and more particularly, to a so-called “shuttle scanning” (serial scanning) type of inkjet recording method and apparatus in which an image is recorded using a pigment-based ink while moving an inkjet head reciprocally in a direction perpendicular to the conveyance direction of the recording medium.
2. Description of the Related Art
Conventionally, an inkjet recording apparatus (inkjet printer) is known, which comprises an inkjet head (ink ejection head) having an arrangement of a plurality of nozzles (ink ejection ports) and which forms images on a recording medium by ejecting ink in the form of liquid droplets from the nozzles toward the recording medium while causing the inkjet head and the recording medium to move relatively with respect to each other.
Various methods are known conventionally as ink ejection methods for an inkjet recording apparatus of this kind. For example, one known method is a piezoelectric method, where the volume of a pressure chamber (ink chamber) is changed by causing a vibration plate forming a portion of the pressure chamber to deform due to deformation of a piezoelectric element (piezoelectric ceramic), ink being introduced into the pressure chamber from an ink supply passage when the volume is increased, and the ink inside the pressure chamber being ejected as a droplet from the nozzle when the volume of the pressure chamber is reduced. Another known method is a thermal inkjet method where ink is heated to generate a bubble in the ink, and ink is then ejected by means of the expansive energy created as the bubble grows.
In an image forming apparatus having an ink ejection head such as an inkjet recording apparatus, ink is supplied to an ink ejection head via an ink supply channel from an ink tank which stores ink, and this ink is ejected by one of the various ejection methods described above. However, it is necessary that ink is ejected stably in such a manner that factors, such as the ink ejection volume, the ejection velocity, the ejection direction, and the shape (volume) of the ejected ink, conform to uniform values at all times.
However, during printing, the nozzles of the ink ejection head are filled with ink at all times, in order that printing can be performed as soon as a printing instruction is issued. Therefore, the ink in the nozzles is exposed to the air, and the ink in nozzles which do not perform ejection for a long period of time dries, the viscosity of the ink increases, and nozzle blockages may occur. Increased viscosity of this kind in the ink meniscus of the nozzles may be a cause of ink ejection failures. Furthermore, there is a possibility that foreign matter, such as dust, and air bubbles which have entered inside the ink supply channel may become trapped and block the supply of ink, leading to the occurrence of ejection defects.
Therefore, conventionally, in response to increased viscosity of the ink in the meniscus region in the nozzles, which can be a cause of ink ejection defects and ink ejection failures, restoration processing has been carried out by purging (dummy ejection or preliminary ejection) or suctioning, in order to expel this ink of increased viscosity from the head, forcibly, at periodic intervals.
In suction-based restoration processing of this kind, the nozzle surface of the inkjet head is covered with a cap and the ink inside the inkjet head is suctioned forcibly by means of a pump, but the ink expelled into the cap by suctioning remains on the nozzle surface immediately after suctioning and may flow in reverse back into the inkjet head. Therefore, a preliminary ejection is carried out after performing a suctioning restoration process.
For example, Japanese Patent Application Publication No. 2004-98626 discloses an inkjet recording apparatus which forms images by using an inkjet head having at least two types of nozzles which eject different ink ejection volumes, including a row of large nozzles and a row of small nozzles. In this apparatus, the amount of floating mist is reduced and the time required for preliminary ejection after suctioning is shortened, by making the number of ejections performed by the large nozzles greater than the number of ejections performed by the small nozzles, or by increasing the ejection frequency of the large nozzles, when preliminary ejection is carried out after suctioning the meniscus.
However, Japanese Patent Application Publication No. 2004-98626 discloses technology relating to the control of preliminary ejection performed by large nozzles and small nozzles after a suctioning restoration process, with the aim of reducing the time required for preliminary ejection after suctioning and preventing the generation of floating mist during preliminary ejection, but it makes no disclosure with respect to purging (preliminary ejection) during a recording scan; in particular when a pigment-based ink is used, there is a problem in controlling preliminary ejection carried out during recording in order to improve ejection stability.